As NSA leaker Edward Snowden is said to be spending his third day in hiding in a Moscow airport, the 30-year-old contractor may have unwittingly become the newest player in a relentless yet relatively little-known espionage war between the U.S. and Russia.

An ABC News review of public reports shows that in the past 16 months alone, at least six people have been accused or convicted of spying for the U.S. in Russia, including two Americans who were kicked out of the country and four Russians purportedly recruited by U.S. intelligence -- all sent to prison. Another American, a lawyer, was reportedly expelled from Russia this May because he rebuffed Russian agents' attempt to recruit him to spy for them.

"Espionage is alive and well" between the old Cold War foes, said David Major, a former senior FBI counter-intelligence officer and now President of the Centre for Counterintelligence and Security Studies, which tracks spy cases the world over.

Some of the cases, like that of blown CIA agent Ryan Fogle, splashed across headlines the world over. But several others, like the case of a Russian intelligence colonel who worked with the CIA and got 18 years behind bars for it, barely made a ripple in American media.

Prior to 2012, the whole world took notice in 2010 when the FBI rounded up 10 undercover Russian agents in America – including the "SoHo Spy" Anna Chapman – but far fewer heard in 2011 when it was revealed a Russian intelligence official in Moscow had given the spy ring up and then fled to the U.S. That man, Col. Alexander Poteyev, reportedly had been recruited by the CIA.

Now with Snowden, a former contractor for the National Security Agency with a head and, reportedly, laptops full of U.S. secrets, Major said the Russians have been handed a victory, even if Snowden insists he's not working with any governments.

"One of the highest targets [for foreign intelligence agencies] has always been the NSA, one of the hardest targets for them ever to penetrate," Major said. "[Russian intelligence] is going to look at this case as an opportunity, as a treasure trove of intelligence that [will be] exploited to the extent that they can, and then when they decide, they'll move on."

While hiding in Hong Kong earlier this month, Snowden revealed himself to be the source of several headline-grabbing reports from The Guardian and The Washington Post revealing what he called "horrifying" U.S. government domestic and foreign surveillance programs. Snowden, who has been charged by the U.S. with espionage, and those he worked with claim there's much more to come to light.

When he was in Hong Kong, Snowden mocked the idea he would defect to China and said he only works "with journalists." After Snowden escaped Hong Kong for Moscow – a move that stunned U.S. officials -- Russia's President Vladimir Putin assured the world Tuesday that his security services have not worked with Snowden.

Such assurances haven't calmed fears from current and former U.S. officials who have told ABC News it would not be difficult for foreign intelligence agents to copy information from the laptops with which Snowden is reportedly traveling, with or without Snowden's permission, or for them to talk directly to Snowden, if need be under the guise of immigration officers. Putin, a former intelligence officer himself, said Snowden is a free man and flatly denied repeated U.S. requests to send him back to the States.

"Why would you want to help?" Major said of Putin's decision not to expel Snowden. "Why wouldn't you want to take advantage of that?"

Whatever the Russians can get from Snowden, if anything, it will be the latest salvo in the decades-long battle over secrets between the U.S. and Russia that in recent years has reached a fevered pitch, harkening back to the days of the Soviet Union and the Berlin Wall.

Cold War Redux: Spying for the U.S. in Mother Russia

The below list is restricted to the most recent cases of alleged professional espionage by the U.S. discovered in Russia, made public since 2012. For more information on the Russian agents caught in the U.S. in 2010, CLICK HERE.

Ryan Fogle: In May 2013 Russian television broadcast a story that resembled a poorly written spy movie spoof: A CIA agent, identified as Ryan Fogle, had been caught red-handed in Moscow with a spy kit including a blond wig, sunglasses, a compass, stacks of cash and a letter intended for a Russian intelligence officer he was trying to recruit. The Russian counter-intelligence agency, the FSB, successor to the infamous KGB, released videotape and photographs showing Fogle in the ill-fitting wig and, later, staring blankly as he was berated by what appeared to be FSB officers for spying in their country. Neither the U.S. State Department or the CIA denied Fogle was a spy, and he was subsequently deported and sent back to the U.S.

At the time, Mark Galeotti, Clinical Professor at NYU's Center for Global Affairs and Russian specialist, told ABC News he was surprised the Russians were making such a public display of what is usually a quiet intelligence agency-to-intelligence agency matter. Major said he believes that was the point all along.

"From day one that case looked to me like a double agent case," Major said, meaning the prospective FSB agent was dangled in front of the CIA as a trap to embarrass the U.S., with props and all. "That's one of the things that counter-intelligence agencies do… They weren't catching a spy, they were sending a message."

Benjamin Dillon: Days after Fogle's unmasking, Russian authorities revealed that another American agent, identified as Benjamin Dillon, was caught and expelled in January. Later, the FSB would reveal the name of the CIA station chief in Moscow, apparently in retaliation for the Fogle debacle.

FSB Col. Valery Mikhailov (Ret.): A little more than a year ago today, a former colonel for the FSB, Valery Mikhailov, was sentenced to 18 years in prison after being convicted of spying for the CIA, according to Russia's state-owned RIA Novosti. According to Russian reports, Mikhailov approached the CIA offering to sell state secrets, but it is unclear when he began spying for the agency.

Col. Vladimir Lazar (Ret.): Now retired, Col. Vladimir Lazar worked in the "military technical headquarters of the general headquarters of the high command" of the Russian military. It was there he had unique access to strategic topographic maps and images, which he copied in 2008 and later sold to an American who worked with U.S. intelligence, RIA Novosti said, earning him 12 years in a Russian prison after he was convicted in May 2012.

Vladimir Nesterets: The FSB announced in February 2012 that Vladimir Nesterets, an engineer at a Russian space facility, pleaded guilty and was sentenced to 13 years in prison for selling information about missile systems to the CIA. The FSB did not say when the alleged sale took place.

Gennady Sipachev: Gennady Sipachev got a relatively light sentence – eight years in prison -- after being convicted of sending "cartographic information" about the Russian Armed Forces to a contact in the U.S. Defense Department over the internet, but that's because he cooperated with authorities and "actively assisted in the investigations and helped to reveal the criminal activities of others," according to RIA Novosti.

The above cases are only the ones that recently have made it to the public light, meaning presumably there are countless other spies and spy catchers that remain slinking through the shadows of Moscow and Washington, more than 20 years since the end of the Cold War.

"Nothing has changed and nothing will change," Major said. "You can have all the kind of reset you want on the political side… the Russian intelligence service is going to conduct intelligence. It's in their national interest to do so. American intelligence is going to do the same thing."